Banishing bacon and burgers from your diet won’t help your heart — at least not if you eat white bread and corn flakes instead.
But you can slash your risk of heart disease if you replace the calories from meat and cheese with salmon, nuts, and veggies stir-fried in olive oil.
That’s the takeaway from a huge study published Monday in the Journal of the American College of Cardiology by researchers from Harvard’s T.H. Chan School of Public Health.
It’s not a big surprise: nutritionists have been decrying the dangers of saturated fat for decades. But last year, a splashy paper turned that advice on its head. It claimed that a reduction in saturated fat intake did not improve cardiovascular health.
Even as nutritionists criticized the science behind the hype, the headlines exploded. “Butter is back,” read one. “Don’t fear the fat,” blazed another.
In the new analysis, a team led by Dr. Frank Hu, codirector of Harvard’s program in obesity epidemiology and prevention, took a deeper dive into diets, examining what people ate instead when they cut down on saturated fat.
That made all the difference. Swapping saturated fats for refined carbohydrates like white rice had no effect on heart disease, while replacing them with unsaturated fats — abundant in nuts, seeds, vegetable oils, and fish — lowered the risk of cardiovascular disease by 15 to 25 percent, the researchers found. Replacing saturated fats with whole grains led to a smaller but still significant reduction in the risk of clogged arteries and heart attack.
“The replacement nutrient matters,” said Harvard epidemiologist Adela Hruby, one of the authors of the study. “People ended up replacing the fat with something that was equally palatable, which was often sugar or refined carbs.”
Hu, Hruby, and their colleagues used data from two massive, Harvard-led investigations that have tracked the health and lifestyle choices of female nurses and male health professionals for decades. They followed close to 85,000 women and 43,000 men, asking the participants every few years to fill in a questionnaire about the kinds of foods they were eating. Not surprisingly, many were replacing saturated fat with refined carbs and sugar.
“We were eating other stuff that was just as bad for us,” said Dr. David Katz, director of the Yale-Griffin Center for Prevention Research.
Not everyone is convinced. Dr. Dariush Mozaffarian, a cardiologist and dean of the Friedman School of Nutrition Science and Policy at Tufts University, took issue with the study design. The authors chose to distinguish between refined carbs and those found in whole grains, but they didn’t break down saturated fats into different types. Some, such as those found in dairy, can actually promote heart health, noted Mozaffarian, one of the coauthors of the controversial 2014 paper suggesting that total saturated fat intake had no effect on heart disease.
Hruby conceded the point: “We don’t eat nutrients in isolation.” But for this study, her team wanted to use the same categories as prior research, to show that the foods you eat instead of saturated fat can have a big effect on health.
Eric Boodman can be reached at eric.boodman@statnews .com. Follow him on Twitter @ericboodman. Follow STAT on Twitter @statnews.